Decoupling amplifying systems



Aug. 30, 1960 H. L. CARTER, JR

DECOUPLING AMPLIFYING SYSTEMS Filed Dec. 14, 1955 i 27 28 29 2576. o'c'u DECOUPLING AMPLIFYING SYSTEMS Howell L. Carter, Jr., Natick, Mass., assignor to Raytheon Company, a corporation of Delaware Filed nec. 14, 195s, ser. No. 553,094 4 claims. (c1. .330;161)

nited States atent This invention relates to a decoupling system, and more specifically to a transformer coupled amplifier wherein a biflar transformer is used for transferring energy from said amplifier, and also for providing a decoupling system for said amplifier.

In this invention there is disclosed a decoupling system comprising an electron discharge device having a plurality of electrodes that include at least a cathode and an anode. The biiilar transformer previously refer-red to comprises a first Winding and a second winding arranged for producing substantially unity coupling therein. In the preferred embodiment the first winding of said bilar transformer will usually be the primary, one end of which is connected to said anode. The second winding is the secondary, one end of which is usually connected to a control grid of the next strage. The opposite end of said secondary is connected to a return path common to said cathode. Said primary winding of said transformer is arranged to appear as a transmission line having a maximum impedance to said secondary Winding at the end where said primary is connected to said anode and a minimum impedance to said secondary winding at the opposite end where said secondary winding is connected to a common return with said cathode. The transformer provides substantially full decoupling by completing a low impedance path from said anode to said cathode through the minimum impedance from said first winding to said second winding. Since the opposite end of said primary winding is usually connected to a common source of potential, a decoupling impedance is connected in series with said primary winding and the operating potential source, thereby effectively isolating said minimum impedance path previously described. The decoupling impedance is preferably made substantially greater than said minimum impedance appearing between said irst Winding and said second winding in order to effectively isolate the decoupling path.

Further objects and advantages of this invention will be apparent as the description progresses, reference being made to the accompanying drawings, wherein:

Fig. 1 is a schematic diagram of a dual stage amplifying system illustrating a rst embodiment of this invention;

Fig. 2 is a schematic diagram of the decoupling system sed in the lament circuits for the stages illustrated in ig. l;

Fig. 3 is a schematic diagram of a dual stage amplifying system illustrating a second embodiment of this invention;

Fig. 4 is a schematic diagram of a dual stage amplifying system illustrating still another embodiment of this invention; and

Fig. 5 is a simplified schematic diagram of the 1decoupling system` that is common to the amplifying systems illustrated in Figs. l, 3 and 4.

Referring now to Fig. 1 there is'shown a 60-megacycle IF lamplifier having two stages and 11. Stage 10 consists of a conventional pentode tube 12l comprising a cathode 13, control grid 14, screen grid 15, suppressor grid 16 and anode 17. Stage 11 is identical to stage 10 and comprises a tube 12a having a cathode 13a, control grid 14a, screen grid 15a, suppressor grid .16a and plate 17a. A biilar transformer 18, which consists of a primary coil 19 and a secondary coil 20, is connected to the output of stage 10. In a similar manner, bilar transformer 21, having a primary 22 Iand a secondary 23, is connected to the output of stage 11. One end of primary coil 19 is connected to anode 17, and the other end of primary winding 19 is connected to a decoupling impedance 24. Screen grid 15 is connected to the junction of prim-ary winding 19 and decoupling impedance 24. In a similar manner, one end of primary winding 22 of bilar transformer 21 is connected to `anode 17a, and the other end of said primary Winding 22 is connected to a second decoupling impedance` 2S. Connected to the junction of primary winding 22 and decoupling impedance 25 is the other end of decoupling impedance 24 and screen grid 15a of stage 11. Impedance 25 is connected in turn to a source of operating potential represented as a battery Z6. The other end of battery 26 is connected to a return path common to cathode 13 of stage 10, cathode 13a of stage 11, one end of secondary winding 20 of transformer 18, and one end of secondary winding 23 of transformer 2.1. The common return path just described is illustrated as a ground return path in order to conform to the common practice of grounding the negative potential of the supply voltage. The band pass of bilar transformers 18 and 21 is made more responsive to the IF frequency that the amplifier is designed for. A bifilar transformer has the characteristic that primary winding 19 of transformer 18 appears as a transmission line when observed from point A. As a result of this transmission line characteristic, there appears a maximum impedance from winding 19 to winding 20 at the end connected to said anode 17 and a minimum impedance from winding 19 to winding 20 at the other end. The decoupling path for tube 12 therefore exists from anode 17 through the minimum impedance appearing between winding 19 and Winding 20 of transformer 18, and hence through the common grounded connection of winding 20 back to cathode 13. Decoupling impedance 24 is preferably constructed of .an impedance substantially greater than said minimum impedance that appears between primary winding 19 and secondary winding 20 in order to effectively isolate the decoupling path previously decribed. In actual operation, it has been found that pri-- mary winding 19 can vary over extremely wide limits from approximately 1A; wave length to 3A; wave length. Under ideal conditions, primary winding 19 would appear as a transmission line of a quarter wave length at the center IF frequency. In such a case, the impedance from primary winding 19 to 20 fat the supply voltage end would be zero, providing maximum decoupling for the plate circuit. The actual value of impedance 24 is a function of the amplification of stages 10 :and 11 which will determine the amount of decoupling that can be tolerated, and also the length of the effective transmission line of prim-ary winding 19 of the IF frequency, since the effective length of the transmission line of winding 19, with respect towinding 20, will determine the exact minimum impedance existing between said windings. The plate decoupling of stage 11 is similar in operation to the decoupling just described for stage 10.

Fig. 2 illustrates a ladder-type decoupling network for the filament circuits that would be adaptable for use in stages 10 and 11 of Fig. l. Filament 26 is connected at one end to an impedance 27, which impedance is preferably constructed of .an inductance in order to minimize power loss'. Filament 28 is connected at one endto a junction of decoupling impedance 27 and decoupling impedance 29. The other end of decoupling impedance 29 is connected to a source voltage not illustrated for operating filaments 26 and 2K8.V A common return path Yfor the operating filament voltage isshown asa ground 3 connection for the source voltage and also for laments 26 and 28. I

Referring now to Fig. 3 there is shown a two-stage IF amplifier comprising stages 30 and 3l. Stage 3f) comprises pentode tube 32 driving a bifilar vtransformer 33. Stage 31 is identical to stage 30, and in a similar manner comprises a pentode tube 34 driving a bifilar transformer 35. The operation of the decoupling network illustrated in Fig. 3 is identical to that described and i1- lustrated in Fig. l with the exception that decoupling impedance 36 of stage 30 and decoupling impedance 37 of stage 31 are connected in parallel to a common voltage source 38. Fig. 3, therefore, illustrates how the invention could be constructed utilizing a parallel connected decoupling impedance, whereas Fig. l illustrates a series, or ladder-type decoupling impedance.

Referring now to Fig. 4, there is shown an IF amplifier similar in operation to that described for the amplifier illustrated in Figs. l and 3, with the exception that the common return path for the supply voltage is at a higher positive potential than the ungrounded side. This type of construction is sometimes called a grounded plate type of amplifier. Fig. 4 illustrates an IF amplifier consisting of stages 39 and 4f). Stage 39 comprises a pentode tube 41 driving a bifilar transformer 42. In a similar manner, 4stage 40 consists of a pentode tube 43 driving a bifilar transformer `44. One end of decoupling impedance 4S is connected to the primary of bifilar transformer 42 in a similar manner as described 4in Fig. l. In a similar manner, decoupling impedance 46 is connected to the primary winding of bifilar transformer 44. The opposite ends of decoupling impedances 45 and 46 are connected to ground, since supply voltage 48 has the positive potential end also grounded, thereby completing a positive potential path for battery 48 to tubes -41 and 43 through the common ground points just described. The operating characteristics of the circuit illustrated in Fig. 4 are identical to that explained for Figs. l and 3.

Referring now to Fig. 5, there is shownan amplified schematic of the decoupling path used in Figs. l, 3 and 4. As mentioned previously, the primary of the bilar transformer is arranged to appear as' a transmission line -49 with reference to line 50 which illustrates the secondary winding of the bifilar transformer. Since one end of the primary winding 49 is connected to an anode and one end of secondary winding 50 is connected to the control grid of the preceding stage, thereby making the transmission line achieved by the bifilar transformer appear as an open-ended transmission line having a 4maximum impedance at one end and a minimum impedance at the other end. It can be seen, therefore, that the closer the transmission line is made to approximate a quarter wave length at the IF frequency, the lower will be the minimum impedance represented as reference 51 appearing between primary winding 49 and secondary winding 50. The complete isolating path therefore consists of an external impedance 52 connected at one end to primary 49, and the other end to the positive potential of a supply source 53. The other end of supply source 53, usually the negative end, is in turn connected `to secondary Sil, which therefore completes the decoupling network.

This completes the description of the embodiment of the invention illustrated herein. However, many modiications and advantages thereof will he apparent to persons skilled in the art without departing from the spirit and scope of this invention. Accordingly, Vit is desired that this invention not be limited to the particular details of the embodiment enclosed herein, except as defined by the appended claims.

What is claimed is:

1. A decoupling system comprising a pair of electron discharge devices, a transformer having a first winding and a second winding arranged for producing substantial-l ly unity coupling therebetween, said transformer Vconnected between 4the Loutput of'one "of -said electron dise charge devices and the input of the other of said electron discharge devices, said first winding having a maximum impedance to said second winding at one end and a minimum impedance to lsaid second winding at the opposite end, and non-capacitive impedance means con- -nected from said opposite end of said first winding to a source of direct energy, said impedance means constituting the sole means for isolating said minimum impedance path from said source, said impedance means having an impedance value substantially greater than said minimum impedance.

2. A decoupling system comprising a pair of electro-n discharge devices, a transformer having a firstwinding and a second winding arranged for producing substantially unity coupling therebetween, said transformer connected between the output ofV o-ne of said electron discharge devices and the input of the other of said electron discharge devices, Said first winding having the characteristics substantially of a quarter-wave length transmission line at the center pass frequency of said transformer, said first winding having a maximum impedance to' said second winding at one end and a minimum impedance to said second winding at the opposite end, and non-capacitive impedance means connected from said opposite end of said first winding to a source of direct energy, said impedance means constituting the sole means for isolating said minimum impedance path from said source, said impedance means having an impedance value substantially greater than said minimum impedance.

3. A decoupling system comprising a pair of electron discharge devices, a transformer having a first winding and a second winding arranged for producing substantially unity coupling therebetween, said first Winding connected to the output of one of said electron discharge devices and said second winding connected to the input of the other of said electron discharge devices, said first winding having a maximum impedance to said second Winding at one end and a minimum impedance to said second winding at the opposite end, and non-capacitive impedance means connected from said opposite'end of said first winding to a source of direct energy, said impedance means constituting the sole means for isolating said minimum impedance path from said source, said impedance means having an impedance value substantially greater than said minimum impedance.

4. A decoupling system comprising a first electron discharge device having at least an anode and a cathode, a second electron discharge device having at least an input electrode, a transformer having a first winding and a second winding arranged for producing `substantially unity coupling therebetween, said first winding connected to the anode of said first electron discharge device, said second winding connected to the input electrode of said second electron discharge device, said first winding having a maximum impedance to said second winding at one end and a minimum impedance to said second winding at the opposite end, said transformer providing a low impedance decoupling path from said anode to said cathode through the minimum impedance path from said first winding to said second winding, and non-capacitive impedance means connected from said opposite end of said first winding to a source of direct energy, said impedance means constituting the sole means for isolating said minimum impedance path from said source, said impedance means having an impedance value substantially greater than said minimum impedance.

References Cited in the file of this patent UNITED STATES PATENTS 1,971,487 IOnes et al V Aug. 28, 1934 2,545,788 McIntosh Mat'. 20', 1951 2,770,686 lHalldcn NOV. 13, 1956 FOREIGN PATENTS A l Y 981,372 Francevsn n..a..a Jan. 10, -1951 

